bikemig
One nice thing about under the chainstay mounted brakes (not that you seem to need it) is that there's nothing to snag on a pannier that's mounted far forward. Especially the old straight arm cantilever brake arms that stuck straight out were prone to getting snagged on a pannier and holding the brake pad(s) against the rim. Not nice if it happened going up a hill.
I had an old Bianchi MTB that had lots of clearance between the rear of the seat tube and the tire even with fenders on. I used to carry an extra water bottle there. It was a 750ml (20 oz) one complete with cage.
I think U-brakes or roller-cam brakes under the chainstays are great for a touring bike.
Cheers